package com.cj.user.service.demo;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @Author cheng jun
 * @Description:
 * @Date 2021/5/13 16:14
 */
public class Demo4 {

    public static void main(String[] args) {
        /*Map<String, Object> map = new HashMap<>(16);
        map.put(null, "111");
        map.put("", "222");
        System.out.println(map);*/
        /*List<String> list = new Vector<>(10);
        list.add(null);
        list.add("bbb");
        System.out.println(list);
        List<String> list2 = new LinkedList<>();
        list2.add(null);
        list2.add("ddd");
        System.out.println(list2);*/
        /*Set<String> set = new HashSet<>();
        set.add(null);
        set.add("eee");
        System.out.println(set);
        Set<String> set2 = new TreeSet<>();
        set2.add(null);
        set2.add("fff");*/
        /*ConcurrentHashMap concurrentHashMap = new ConcurrentHashMap();
        concurrentHashMap.put("111", "aaa");
        System.out.println(concurrentHashMap);*/
        //String a = null;
        //System.out.println(a.hashCode());
    }
}
